Joint repair, or arthroplasty, is a surgical intervention for repairing defects or injuries of a joint. The goal is to restore as much normal function as possible while at the same time reducing or eliminating pain and discomfort. Joint repairs allow patients to regain mobility, continue contributing to society and enjoy a greater quality of life.
Arthroplasty attempts to correct how two bones interact with one another. For example, in a hip the femoral head 6 fits into the acetabulum 3 of the pelvis 1 creating a ball and socket type joint. The movement of the femur 2 in the pelvis 1 is constrained by both the bony-to-bony interaction as well as the function of the soft tissue (ligaments and muscle) attached to both bony anatomies. Arthroplasty involves resurfacing or replacing the natural surfaces of the bones where they interact (the articular surface). For example, referring to FIG. 2, when performing hip arthroplasty a surgeon replaces or resurfaces the femoral head 6 and acetabulum 3 with artificial implants. To help restore function the soft tissue may also be modified, such as through a partial release of its attachment to bone.
Intervention to correct problems of a joint suffers from difficulty in finding an optimal implant placement including position and orientation. Problems arising from incorrect placement may involve, among other symptoms, post surgical pain, limited range of motion, dislocation, post surgical fracture, premature implant failure, and adverse biologic response consequent to any of the preceding problems.
The extent of the problem is evidenced in high revision rates. The majority of arthroplasties (86%) performed in U.S. are on the hip or knee (American Academy of Orthopaedic Surgeons, “Musculoskeletal Conditions in the United States”, p. 121, 1999). According the American Academy of Orthopaedic Surgeons, 54,000 of the total hip and knee procedures done in the U.S. each year are revision surgeries (American Academy of Orthopaedic Surgeons Bulletin, “Number of arthroplasties to increase dramatically”, Vol. 50, No. 1, 2002).
Dislocation following arthroplasty is a major factor in early failure with an incidence rate, for example, of 3-5% for hips (for discussion see McCullum, D E, W J Gray, “Dislocation After Total Hip Arthroplasty—Causes and Prevention”, Clinical Orthopaedics and Related Research, December (261), pp. 159-170, 1990). The common reason for dislocation is the position and orientation of the artificial implants, particularly of the acetabulum implant in hip arthroplasty (for discussion see Lewinnek et al., “Dislocation after Total Hip-Replacement Arthroplasties”, Journal Bone Joint Surgery, 60-A(2), pp. 217-220, 1978). When the implants are not correctly placed, impingements 4 between the implant components and/or anatomy can occur. These points of impingement cause a lever effect and potentially result in dislocation. Besides being painful and stressful for the patient, it also leads to abductor tissue damage, which has a detrimental long-term effect on the stability of the hip joint.
A number of methods and apparatuses for assisting in arthroplasties have been developed. These methods and apparatuses include mechanical jigs and computer-assistance (both image-based and imageless). A common aspect is the use of an anatomic reference such as the sagittal and coronal planes of the patient, or the pelvic plane as defined by the pubic tubercles 85, 86 and anterior superior iliac spines 7, 8.
Mechanical guides attempt to address the problem by providing surgical tools which, when placed in a specific manner provide a referencing system for determining implant placement (for discussion see Eggli et al., “The value of preoperative planning for total hip arthroplasty”, Journal Bone Joint Surgery, 80-B(4), pp. 382-390, 1998). These solutions can suffer from one or more of the following problems.
They are based on standardized placement specifications that may not apply to an actual patient. The guides depend on precise, but difficult, placement within anatomy. The external frame of reference can change dramatically based on patient anatomy, positioning and surgical approach. They typically do not allow for soft tissue effects. The guides provide a static placement for a problem that is inherently kinematic in nature. The guides provide limited flexibility for anatomical variability.
Image-based computer assisted solutions also exist. These solutions typically use either CT (for discussion see DiGioia et al., “HipNav Technical Paper”, Centre for Medical Robotics and Computer Assisted Surgery) or fluoroscopy (Tannast et al., “Accuracy and potential pitfalls of fluoroscopy-guided acetabular cup placement”, Computer Aided Surgery, Vol. 10, Issue 5-6, pp. 329-336) to capture images of the anatomy. Used in conjunction with a spatial tracking device, the images are then used to anatomically plan the implant placement, in either a manual or semi-automatic manner. These systems then provide the surgeon with guidance to transfer the planned placement onto the patient anatomy.
3D solutions (typically based on Computer-Tomography or Magnetic Resonance Imaging) can have one or more of the following limitations. They require pre-surgical scanning of the patient consuming more time, increasing cost and exposing the patient to additional radiation. Planning based on scans and reconstruction of the bony anatomy fail to account for the important and significant contribution of soft tissue to the function of the joint. Three-dimensional scans are typically used to create a surface model of the anatomy. This adds time and has potential error associated with it. Complex, time consuming and potentially error-prone registration of the patient to the scan must be performed intra-operatively. A pre-surgical planning step is often used with CT-based systems. Such planning is scheduled separately from the surgery and consumes more time and thus increases cost. Pre-operative imaging does not allow for intra-operative updating.
2D (typically fluoroscopy) solutions can have one or more of the following limitations. The prescribed images can be difficult to obtain (e.g., lateral image of the hip). There is additional radiation exposure to the patient and operating room staff. Fluoroscopy requires tracking of the c-arm (x-ray image intensifier) and image processing to account for image distortion and to characterize the c-arm geometry. The hardware necessary to do this increases cost. The additional setup can be complicated and time-consuming. The image processing requires use of software algorithms that must be written, maintained and presents another opportunity for introducing error. Picking 3D anatomical landmarks from 2D images, particularly on complex anatomy and/or lower quality images is difficult and error-prone.
Non-image, computer assisted solutions also exist (for discussion see Jansen et al., “Computer-Assisted Hip Replacement Surgery, patent US2004/0230199-A1). They make using of spatial tracking technology to detect the location of the patient and surgical instruments. These solutions attempt to solve the issues involved with image-based solutions by having the surgeon palpate specific anatomical points in order to define properties of the anatomy (e.g., the pelvic plane) and/or require ‘painting’ of the local bony anatomy in order to morph standardized anatomical models to the patient's anatomy. Palpation of anatomy to define anatomical properties (axes, planes, etc.) has difficulty in accurately palpating anatomical features, e.g., the right 85 and left pubic tubercles 86 and right 7 and left anterior superior iliac spine (ASIS) 8 for determining the pelvic plane. It can also have an increased risk of infection from percutaneous palpations outside the immediate joint replacement site. Extensive ‘painting’ of the local anatomy with a spatially tracked probe has one or more of the following shortcomings as well. Inaccessible anatomy for ‘painting’ (particularly with minimally invasive approaches). Painting is time consuming, which increases the procedure time. There is difficulty in maintaining probe-to-anatomy contact.
Current image-based and non-imaging computer assisted solutions attempt to define anatomical properties (axes, planes, etc.) for the purposes of guiding the user, and face one or more of the following problems. Solutions using anatomical properties prescribe implant placement based on standardized values derived from a large population. Standardized orientations are derived by using a sample population to determine what orientations result in the fewest complications and failures. These are defined relative to a standardized frame of reference, further removing the solution from the patient specific joint function. Not being patient specific they are not necessarily ideal, or even correct, for an individual. Whether point picking in images or palpating anatomy, the process for providing the inputs to calculate the anatomical properties is often difficult and error-prone. The anatomical properties are based on bony anatomy and fail to account for the critical contribution of soft tissue to the behaviour of joints.
Alternative methods and apparatuses for assisting in implant placement are desirable to assist in addressing one or more of the issues with existing methods and apparatuses.